1. Field of the Invention
The present invention relates to a laminated iron core manufacturing method and a blanking die apparatus.
2. Description of the Related Art
Generally, a blanking die apparatus 80, as shown in FIG. 4, includes an upper die tool 82 and a lower die tool 83 connected to each other by multiple guide posts 81 and also has multiple machining stations S1 to S6 (the number of machining stations is arbitrary) respectively for blanking a belt-shaped workpiece 84 (for example, an electromagnetic steel plate) progressively. Each of the machining stations S1 to S6 has a die 85 fixed to the lower die tool 83 and a punch 87, paired with the die 85, fixed to the upper die tool 82, while the punch 87 paired with the die 85 constitutes a cutting tool. The respective machining stations S1 to S6 also have a stripper 88 hanging down from the upper die tool 82 for pressing and holding the workpiece 84 in blanking process. Here, in FIG. 4, the dies 85 equipped in the respective machining stations S1 to S6 are held by a die holder 86 and are fixed to the lower die tool 83, while the strippers 88 equipped in the respective machining stations S1 to S6 hang down from the upper die tool 82.
The workpiece 84 progressively fed to the blanking die apparatus 80 is subjected to blanking in the machining stations S1 to S5 sequentially, is subjected to contour blanking in the final machining station S6 (blanking station), and core pieces blanked in the machining station S6 are crimped and laminated, thereby manufacturing a laminated iron core.
The blanking die apparatus in the related art, however, has a trouble caused by an eccentric load applied in blanking. For example, when the upper die tool is slightly inclined relative to the lower die tool due to the eccentric load, a clearance set between the paired punch and die is varied to cause the punch and die to break, thereby incurring the shortened life of the cutting tool.
Thus, there is set a blanking layout (a discretely arranged state of the machining stations) in which the respective blanking loads of the machining stations for performing their specific blanking processes are previously calculated in order to prevent the blanking loads from being biased forward (on the upstream side in the workpiece progressive feeding direction) or backward (on the downstream side in the progressive feeding direction) over the whole length of the blanking die apparatus. Also, it is desired that the center position of the blanking load (which is hereinafter called the load center position) applied to the whole of the blanking die apparatus coincides with the center position of the whole length of the blanking die apparatus (which is hereinafter called the apparatus center position). Thus, even when perfect coincidence is difficult, the load center position and apparatus center position are normally designed such that they near each other as much as possible.
Here, when the core pieces of a small-diameter laminated iron core to be applied to a small-sized motor for use in a household appliance and the like are blanked from a workpiece using a blanking die apparatus, especially, when the core pieces of laminated iron cores respectively constituting a rotor and a stator are blanked sequentially using a single blanking die apparatus, it is easy to provide a blanking layout in which the load center position and apparatus center position approach each other relatively. However, for example, in a blanking die apparatus which blanks only core pieces for forming a laminated iron core constituting a rotor or a stator, the total of the blanking loads of the machining stations situated nearer to the import side of the workpiece than the apparatus center position for performing the former processes for forming the core pieces is larger than the total of the blanking loads of the machining stations situated nearer to the export side of the workpiece than the apparatus center position for performing the latter processes for forming the core pieces, thereby increasing a gap between the load center position and apparatus center position to incur a load distribution in which an eccentric load is easy to occur.
To solve such eccentric load applied to the blanking die apparatus, for example, in JP-A-2001-162336, as shown in FIG. 5, there is disclosed a technology that, with respect to an eccentric load generated by a bending punch 88 used in a bending process serving as the final process of the machining operations, an inclination preventive punch 91 is provided on the entrance side of a workpiece 90 in a blanking die apparatus 89, and the bending punch 88 and inclination preventive punch 91 are operated simultaneously to thereby cancel the eccentric load.